Method and apparatus for determining reference picture set of image

ABSTRACT

A method of determining a reference picture set (RPS), which is a set of reference pictures used in predictive decoding of a current picture that is to be decoded includes: obtaining a flag indicating whether the RPS is determined based on picture order count (POC) values of the current picture and a previous picture or whether the RPS is determined based on an index of a reference RPS, which is an identification value of the reference RPS that is one of pre-defined RPSs and is referred to in determining the RPS, and a delta RPS that is a difference value between a POC vale of a reference picture included in the reference RPS and a POC value of a reference picture included in the RPS; and determining the RPS according to a value of the flag.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.16/799,362 filed on Feb. 24, 2020, which is a Continuation of U.S.application Ser. No. 16/207,656 filed on Dec. 3, 2018, now U.S. Pat. No.10,609,378 issued on Mar. 31, 2020, which is a Continuation of U.S.application Ser. No. 14/394,820 filed on Oct. 16, 2014, now U.S. Pat.No. 10,171,811 issued on Jan. 1, 2019, which is a national stageapplication of International Application No. PCT/KR2013/003181 filed onApr. 16, 2013, which claims the benefit of U.S. Provisional Application61/624,468, filed on Apr. 16, 2012, in the United States Patent andTrademark Office, the disclosures of which are herein incorporated byreference in their entireties.

BACKGROUND 1. Field

One or more exemplary embodiments relate to a method and apparatus fordetermining a reference picture set (RPS) which is a set of referencepictures that are used in predictive decoding of a current picture thatis to be decoded.

2. Related Art

Recently, with the development of digital display technology and theadvent of high-quality digital televisions (TVs), a new codec forprocessing a large amount of video data has been proposed. Informationof reference pictures which are used in predictive decoding of a currentpicture can be encoded and transferred to a decoding portion. Thedecoding portion can perform predictive decoding of the current pictureby using the transferred information of the reference pictures.

SUMMARY

Exemplary embodiments relate to a method and apparatus for determining areference picture set (RPS) which is a set of reference pictures thatare used in predictive decoding of a current picture.

According to one or more exemplary embodiments, a method of determiningan RPS which is a set of reference pictures that are used in predictivedecoding of a current picture includes: determining whether or not todetermine the RPS based on a delta RPS which is a difference valuebetween a picture order count (POC) value of a reference pictureincluded in a reference RPS which is one of pre-defined RPSs and isreferred to in determining the RPS and a POC value of a referencepicture included in the RPS; and determining the RPS based on a resultof the determining.

The determining of the RPS may include: obtaining a flag indicatingwhether the RPS is determined based on the delta RPS which is determinedbased on POC values of the current picture and a previous picture orwhether the RPS is determined based on an index of the reference RPS,which is an identification value of the reference RPS, and the deltaRPS; and determining the RPS according to a value of the flag.

The RPS may be an RPS which is not pre-defined in a sequence parameterset (SPS).

The determining of the RPS may include: determining the delta RPS of theRPS, based on a difference value between the POC value of the currentpicture and the POC value of the previous picture; and determining theRPS based on the delta RPS of the RPS and an RPS used in predictivedecoding of the previous picture.

The determining of the RPS may include: obtaining the delta RPS and theindex of the reference RPS; obtaining the reference RPS based on theindex of the reference RPS; and determining the RPS based on a value ofthe delta RPS added to POC values of the reference pictures included inthe reference RPS.

The method may include: determining the RPS which is a set of referencepictures used in predictive decoding of a current picture that is to bedecoded; determining whether to signal the RPS based on a delta RPSwhich is a difference value between a picture order count (POC) value ofa reference picture included in a reference RPS which is one ofpre-defined RPSs and is referred to in the determining of the RPS and aPOC value of a reference picture included in the RPS; and signaling theRPS based on a result of the determining.

The signaling of the RPS may include: determining whether the RPS isdetermined based on the delta RPS which is determined based on POCvalues of the current picture and a previous picture or whether the RPSis determined based on an index of the reference RPS, which is anidentification value of the reference RPS, and the delta RPS; and addinga flag to a predetermined domain of a bit stream according to a resultof the determining.

The RPS may be an RPS which is not pre-defined in a sequence parameterset (SPS).

When the RPS is obtained based on the POC values of the current pictureand the previous picture, the delta RPS of the RPS may be determinedbased on a difference value between the POC value of the current pictureand the POC value of the previous picture and the RPS may be obtainedbased on the delta RPS of the RPS and an RPS used in predictive decodingof the previous image.

The method may further include adding the delta RPS and the index of thereference RPS to the predetermined domain of the bit stream, when theRPS is obtained based on the delta RPS and the index of the referenceRPS, and the RPS may be obtained based on the reference RPS obtainedbased on the index of the reference RPS and the delta RPS.

According to the one or more of the above exemplary embodiments, a videodecoding apparatus may obtain the delta RPS by using the POC differencevalue between the current picture and the previous picture, without theneed of the delta RPS being explicitly encoded and transferred via thevideo encoding apparatus, in order to signal the delta RPS to obtain theRPS to be used in predictive decoding of the current picture. Therefore,the number of bits encoded in the video encoding apparatus may bereduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are block diagrams of an internal structure of a videoencoding apparatus according to an exemplary embodiment.

FIGS. 2A and 2B are block diagrams of an internal structure of a videodecoding apparatus according to an exemplary embodiment.

FIG. 3 is a block diagram of an internal structure of a picture encodingunit according to an exemplary embodiment.

FIG. 4 is a block diagram of an internal structure of a picture decodingunit according to an exemplary embodiment.

FIGS. 5 and 6 are flowcharts illustrating a method of signaling areference picture set (RPS) according to an exemplary embodiment.

FIGS. 7 and 8 are flowcharts illustrating a method of determining an RPSaccording to an exemplary embodiment.

FIG. 9 is a view of an example of a sequence parameter set (SPS)according to an exemplary embodiment.

FIG. 10 is a view of an example of a slice header according to anexemplary embodiment.

FIG. 11 is a view of an example of a short term RPS according to anexemplary embodiment.

FIGS. 12A and 12B are views of an example of an RPS of picturesaccording to an exemplary embodiment.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, exemplary embodiments will be described in detail withreference to the attached drawings. Detailed descriptions of relatedwell known functions or configurations will be omitted so as not toobscure the description of the exemplary embodiments. Like referencenumerals in the drawings denote like elements.

The terms and words which are used in the present specification and theappended claims should not be limited to their common or dictionarymeanings, but should be construed as having a meaning and concept fit tothe technological concept and scope and of the exemplary embodiments.The presented exemplary embodiments and structures described in thedrawings of the present specification are just exemplary, and they donot represent the entire technological concept and scope. Therefore, itshould be understood that there can be many equivalents and modifiedembodiments that can substitute those described in this specification.

The exemplary embodiments may be applied to an encoding standard basedon an arbitrary intra frame and an inter frame. The term “picture” usedthroughout the present specification is an inclusive term to denotevarious forms of video image information that may be known in therelated art, such as a “frame,” a “field,” and a “slice.”

A reference picture may be a picture that may be used forinter-prediction of a block in a current picture.

Generally, an encoding portion may identify reference pictures by usinga picture order count (POC) value. The POC value represents a relativeorder of display of corresponding pictures. For example, a picturehaving a low POC value may be displayed earlier than a picture having ahigh POC value. The order of display and an order of decoding ofpictures are different. The picture having the low POC value may not bedecoded earlier than the picture having the high POC value. Also, thepicture having the low POC value may be decoded earlier than the picturehaving the high POC value.

According to an exemplary embodiment, a description is made based on aHigh Efficiency Video Coding (HEVC) standard. However, it is not limitedthereto, and may be applied to other video coding technologies. Forexample, a reference picture set (RPS) is described based on the HEVCstandard, but the RPS may be applied to other standards.

Hereinafter, one or more exemplary embodiments will be described morefully with reference to the accompanying drawings.

FIGS. 1A and 1B are block diagrams of an internal structure of a videoencoding apparatus 100 according to an exemplary embodiment.

Referring to FIG. 1A, the video encoding apparatus 100 may include anRPS determination unit 101 (e.g. an RPS determiner, etc.) and asignaling method determination unit 102 (e.g., a signaling methoddeterminer, etc.).

An RPS refers to a set of reference pictures which are capable of beingused in predictive decoding of a current picture that is to be decoded.The RPS may be defined in a sequence parameter set (SPS) or a sliceheader. The SPS is header information including information regardingencoding of a sequence, such as a profile, a level, and the like. TheSPS may include a plurality of RPSs that are capable of being identifiedas indexes. The slice header may include an additionally defined RPS inaddition to the RPS defined in the SPS. The additionally defined RPS maybe used in a picture corresponding to the slice header including theRPS.

The reference pictures included in the RPS may be indicated as a pictureorder count (POC) value based on the current picture. That is, when aPOC value of the current picture for which the RPS may be used is set to0, a POC value of the reference picture may be indicated. Although theremay be a short term RPS and a long term RPS, the RPS hereinafter may bethe short term RPS.

A method of defining the RPS in the slice header in the video encodingapparatus 100, that is, a method of signaling an RPS, includes aninter-RPS prediction method. According to the inter-RPS predictionmethod, the video encoding apparatus 100 may signal the RPS in the sliceheader to obtain an RPS to be used in predictive decoding of the currentpicture by referring to one of RPSs pre-defined in the SPS. In detail,the video encoding apparatus 100 may signal the RPS by adding a deltaRPS of the RPS and an index of an RPS that may be referred to indetermining the RPS to a bit stream. The RPS may be obtained in adecoding portion by adding the delta RPS, which is a difference betweenthe reference RPS and the RPS to the reference RPS. That is, the RPS maybe obtained by adding the delta RPS to each of POC values of referencepictures included in the reference RPS. The reference RPS is a valuepre-defined in the SPS and may be identified as an index.

According to an exemplary embodiment, the delta RPS of the RPS that isto be used in predictive decoding of the current picture may be obtainedby the fact that the delta RPS of the RPS that is to be used inpredictive decoding of the current picture is the same as a differencebetween a POC value of the current picture and a POC value of a previouspicture. Here, the previous picture may refer to a picture previous tothe current picture, on a basis of an order of encoding. This is becausethe reference picture of the current picture should be a referencepicture of a picture previously output or a reference picture of apicture previously decoded. Thus, according to the exemplary embodiment,the delta RPS of the RPS may be obtained by a POC difference between thepreviously decoded picture and the current picture. Accordingly, thevideo encoding apparatus 100 may signal the RPS used in predictivedecoding of the current picture without adding the delta RPS and theindex of the reference RPS to the bit stream. Here, the decoding portionmay obtain the delta RPS of the RPS by the difference between the POCvalues of the current picture and the previous picture and obtain an RPSused in predictive decoding of the previous picture, in order to obtainthe RPS to be used in predictive decoding of the current picture fromthe delta RPS and the RPS used in predictive decoding of the previouspicture.

The video encoding apparatus 100 according to the exemplary embodimentmay determine the RPS to be used in predictive decoding of the currentpicture and may add a flag to the bit stream based on the method ofsignaling the RPS. Also, the video encoding apparatus 100 may encode thecurrent picture by using the determined RPS.

The RPS determination unit 101 may determine the RPS to be used inpredictive decoding of the current picture. The determined RPS may besignaled according to a signaling method determined by the signalingmethod determination unit 102.

The signaling method determination unit 102 may determine whether tosignal the RPS based on the delta RPS and may signal the RPS based on aresult of the determination, in order to signal the RPS determined bythe RPS determination unit 101.

Referring to FIG. 1B, the video encoding apparatus 100 according to thepresent embodiment may include an RPS determination unit 110 (e.g., anRPS determiner, etc.), a signaling method determination unit 120 (e.g.,a signaling method determiner, etc.), a flag adding unit 130 (e.g., aflag adder, etc.), a picture encoding unit 140 (e.g., a picture encoder,etc.) and an output unit 150 (e.g., an output, etc.). The RPSdetermination unit 110 and the signaling method determination unit 120of FIG. 1B respectively correspond to the RPS determination unit 101 andthe signaling method determination unit 102 of FIG. 1A, and thus, theirdetailed descriptions will be omitted. The RPS determination unit 110may determine the RPS to be used in predictive decoding of the currentpicture.

The signaling method determination unit 120 may determine the method ofsignaling the RPS to be used in predictive decoding of the currentpicture. The signaling method determination unit 120 may determinewhether to determine the RPS based on the delta RPS and may determinethe method of signaling the RPS based on a result of the determination.According to an exemplary embodiment, there are two methods of signalingthe RPS based on the delta RPS. According to the first signaling method,in the video encoding apparatus 100, the decoding portion may determinethe delta RPS based on POC values of the current picture and theprevious picture and may signal the RPS to determine the RPS to be usedin predictive decoding of the current picture, based on the determineddelta RPS. Also, according to the second signaling method, in the videoencoding apparatus 100, the decoding portion may signal the RPS todetermine the RPS to be used in predictive decoding of the currentpicture based on the delta RPS and an index of the reference RPS used inpredictive decoding of the current picture. The decoding portion mayobtain the reference RPS by using the index of the reference RPStransferred from the video encoding apparatus 100, and may determine theRPS to be used in predictive decoding of the current picture based onthe delta RPS and the reference RPS.

The flag adding unit 130 may add a flag to a bit stream according to asignaling method determined by the signaling method determination unit120. In detail, the flag adding unit 130 may add flag values, whichdiffer according to the first signaling method and the second signalingmethod, to the bit stream For example, the flag adding unit 130 may setthe flag value to 1 in the case where the RPS to be used in predictivedecoding of the current picture is signaled by the first signalingmethod. The flag adding unit 130 may set the flag value to 0 in the casewhere the RPS to be used in predictive decoding of the current pictureis signaled by the second signaling method. Thus, the decoding portionmay determine the signaling method based on the flag value and determinethe RPS to be used in predictive decoding of the current picture basedon the determined signaling method.

The picture encoding unit 140 may encode the current picture by usingthe RPS determined by the RPS determination unit 110. The encodedpicture may be converted to a bit stream to be transferred to a videodecoding apparatus 200 via the output unit 150.

The output unit 150 may output the encoded picture and a bit streamassociated with information necessary for decoding the picture. The flagadded to the bit stream by the flag adding unit 130 is the informationnecessary for decoding pictures and may be output by the output unit 150by being added to the bit stream.

FIGS. 2A and 2B are block diagrams of an internal structure of the videodecoding apparatus 200 according to an exemplary embodiment.

Referring to FIG. 2A, the video decoding apparatus 200 may include anRPS determination unit 201 (e.g., an RPS determiner, etc.).

The RPS determination unit 201 may determine whether to determine an RPSbased on a delta RPS and determine the RPS based on a result of thedetermination, in order to determine the RPS which is a set of referencepictures that are used in predictive decoding of a current picture.

Referring to FIG. 2B, the video decoding apparatus 200 may include areceiving unit 210 (e.g., a receiver, etc.), a flag obtaining unit 220(e.g., a flag obtainer, etc.), an RPS determination unit 230 (e.g., anRPS determiner, etc.), and a picture decoding unit 240 (e.g., a picturedecoder, etc.). The RPS determination unit 230 of FIG. 2B corresponds tothe RPS determination unit 201 of FIG. 2A, and thus, its descriptionwill not be repeated here.

The receiving unit 210 may receive a bit stream with respect to anencoded picture to perform parsing.

The flag obtaining unit 220 may obtain a flag to obtain an RPS in thebit stream for which the parsing is performed. According to a value ofthe flag, the RPS to be used in predictive decoding of the currentpicture is determined based on POC values of the current picture and aprevious picture, according to the first signaling method.Alternatively, the RPS to be used in predictive decoding of the currentpicture is determined based on the delta RPS and an index of a referenceRPS transferred from the video encoding apparatus 100, according to thesecond signaling method.

The RPS determination unit 230 may determine the RPS to be used inpredictive decoding of the current picture according to the flagobtained by the flag obtaining unit 220. According to the firstsignaling method, the RPS determination unit 230 may determine the deltaRPS of the RPS based on a difference value between the POC values of thecurrent picture and the previous picture, and may determine an RPS usedin predictive decoding of the previous picture. In addition, the RPSdetermination unit 230 may add the determined delta RPS to the RPS usedin predictive decoding of the previous picture in order to determine theRPS to be used in predictive decoding of the current picture. That is,the RPS may be determined based on a value of the delta RPS added toeach of POC values of reference pictures included in the RPS used inpredictive decoding of the previous picture. Also, according to thesecond signaling method, the RPS determination unit 230 may obtain areference RPS by using an index of the reference RPS transferred fromthe video encoding apparatus 100. Also, the RPS determination unit 230may obtain the RPS to be used in predictive decoding of the currentpicture by adding the delta RPS transferred from the video encodingapparatus 100 to the reference RPS. That is, the RPS may be determinedbased on the value of the delta RPS added to each of the POC values ofthe reference pictures included in the reference RPS.

The picture decoding unit 240 may decode a picture by using the RPSdetermined by the RPS determination unit 230.

FIG. 3 is a block diagram of an internal structure of a picture encodingunit 300 according to an exemplary embodiment.

Referring to FIG. 3, the picture encoding unit 300 may include amovement estimation unit 301 (e.g., a movement estimator, etc.), amovement compensation unit 302 (e.g., a movement compensator, etc.), anintra-prediction unit 303 (e.g., an intra-predictor, etc.), a convertingunit 305 (e.g., a converter, etc.), a quantization unit 306 (e.g., aquantizer, etc.), an entropy encoding unit 307 (e.g., an entropyencoder, etc.), a reverse quantization unit 308 (e.g., reversequantizer, etc.), a reverse converting unit 309 (e.g., a reverseconverter, etc.), a deblocking unit 310 (e.g., a deblocker, etc.), and aloop filtering unit 311 (e.g., a loop filterer, etc.). The pictureencoding unit 300 of FIG. 3 may correspond to the picture encoding unit140 of FIG. 1.

The movement estimation unit 301 may estimate the movement of thecurrent picture by using reference pictures included in an RPS withrespect to a current picture which is a picture currently input from theoutside among pictures forming a video.

The movement compensation unit 302 may generate a predictive picture ofthe current picture by using the reference pictures included in the RPSwith respect to the current picture. In more detail, the movementcompensation unit 302 may generate the predictive picture of the currentpicture by using the movement of the current picture, which is estimatedby the movement estimation unit 301.

The intra-prediction unit 303 may predict each of intra mode blocksamong blocks forming the current picture to generate the predictivepicture of the current picture.

The converting unit 305 may convert a residual picture, which iscalculated by subtracting the predictive picture from the currentpicture, from a spatial domain to a frequency domain. For example, theconverting unit 305 may convert the residual picture from the spatialdomain to the frequency domain by using an integer transform of thediscrete Hadamard transform (DHT) and discrete cosine transform (DCT).

The quantization unit 306 may quantize frequency coefficients of theresidual picture converted by the converting unit 305.

The entropy encoding unit 307 may generate a bit stream byentropy-encoding results of quantization by the quantization unit 306.In particular, the entropy encoding unit 307 may entropy encodeinformation for video decoding, for example, RPS information used ininter-prediction, movement vector information, location information ofneighboring blocks used in intra-prediction, in addition to the resultsof quantization by the quantization unit 306.

The reverse quantization unit 308 may reverse-quantize the results ofquantization by the quantization unit 306.

The reverse converting unit 309 may convert results of quantization bythe reverse quantization unit 308. That is, the reverse converting unit309 may convert conversion coefficient values from a frequency domain toa spatial domain to restore the residual picture of the current pictureand the predictive picture.

The deblocking unit 310 and the loop filtering unit 311 may adaptivelyperform filtering for the picture restored by the reverse quantizationunit 308.

FIG. 4 is a block diagram of an internal structure of a picture decodingunit according to an exemplary embodiment.

Referring to FIG. 4, the picture decoding unit 400 may include a parsingunit 401 (e.g., a parser, etc.), an entropy decoding unit 403 (e.g., anentropy decoder, etc.), a reverse quantization unit 405 (e.g., a reversequantizer, etc.), a reverse converting unit 407 (e.g., a reverseconverter, etc.), an intra-prediction unit 409 (e.g., anintra-predictor, etc.), a movement compensation unit 415 (e.g., a motioncompensator, etc.), a deblocking unit 411 (e.g., a deblocker, etc.), anda loop filtering unit 413 (e.g., a loop filterer, etc.). The picturedecoding unit 400 of FIG. 4 may correspond to the picture decoding unit240 of FIG. 2.

The parsing unit 401 may perform parsing with respect to data of anencoded picture which is to be decoded and with respect to informationrelated to decoding, which is necessary for encoding, from a bit stream.

The entropy decoding unit 403 may restore information for video decodingby entropy decoding the bit stream.

The reverse quantization unit 405 may restore conversion coefficientvalues by reverse quantizing values restored by the entropy decodingunit 403.

The reverse converting unit 407 may restore a residual picture of acurrent picture and a predictive picture by converting the conversioncoefficient values restored by the reverse quantization unit 402 from afrequency domain to a spatial domain.

The intra-prediction unit 409 may generate the predictive picture of thecurrent picture by predicting a value of a block of the current picturefrom a value of a restored block located neighboring a block of thecurrent picture. The restored picture may be generated by adding theresidual picture to the predictive picture.

The movement compensation unit 415 may generate the predictive pictureof the current picture from reference pictures included in an RPS to beused in predictive decoding of the current picture. The restored picturemay be generated by adding the residual picture to the predictivepicture.

The deblocking unit 411 and the loop filtering unit 413 may adaptivelyperform filtering for the restored picture.

FIG. 5 is a flowchart illustrating a method of signaling an RPSaccording to an exemplary embodiment.

Referring to FIG. 5, the picture encoding apparatus 100 according to anexemplary embodiment may determine an RPS to be used in predictivedecoding of a current picture in operation S501. That is, the pictureencoding apparatus 100 may determine the RPS which is a set of picturesto be referred to in encoding the current picture. The picture encodingapparatus 100 may determine the RPS by referring to an index of one ofRPSs defined in an SPS or may additionally define an RPS in a sliceheader in addition to the RPS defined in the SPS. According to anexemplary embodiment, in the case where an additional RPS is defined inthe slice header in addition to the RPS defined in the SPS, the RPS maybe defined by first and second signaling methods that will be describedlater.

The picture encoding apparatus 100 may determine whether the RPS isobtained based on a delta RPS in operation S503.

The picture encoding apparatus 100 may signal the RPS based on a resultof the determination of operation S503, in operation S505.

FIG. 6 is a flowchart illustrating a method of signaling an RPSaccording to an exemplary embodiment.

Referring to FIG. 6, the picture encoding apparatus 100 may signal anRPS to be used in predictive encoding of a current picture based on adelta RPS, in operation S601.

In the case where the picture encoding apparatus 100 signals the RPSbased on the delta RPS, the picture encoding apparatus 100 may determinewhether the RPS is obtained based on a difference value between POCvalues of a current picture and a previous picture in order to signalthe RPS to be used in predictive decoding of the current pictureaccording to the first method of signaling the RPS to be used inpredictive decoding of the current picture, or whether the RPS isobtained based on the delta RPS of the RPS and an index of a referenceRPS that may be referred to in determining the RPS in order to signalthe RPS to be used in predictive decoding of the current pictureaccording to the second method of signaling the RPS to be used inpredictive decoding of the current picture, in operation S603. Here, thereference RPS may be one of RPSs pre-defined in an SPS and may beidentified as an index of the reference RPS. The picture encodingapparatus 100 may determine one of the two signaling methods, which hasbetter encoding efficiency. For example, the picture encoding apparatus100 may determine the method of signaling the RPS based on a ratedistortion cost. When the RPS is signaled by the first signaling methodaccording to which the RPS is obtained based on the difference valuebetween the POC values of the current picture and the previous picturein operation S605, a flag having a value of 1 may be added to apredetermined domain of a bit stream in operation S607. By this, the RPSto be used in predictive decoding of the current picture may besignaled.

When the RPS to be used in predictive decoding of the current picture issignaled by the second signaling method according to which the delta RPSand the index of the reference RPS are signaled in operation S605, aflag having a value of 0 may be added to a predetermined domain of thebit stream in operation S609.

According to the second signaling method, the picture decoding apparatus200 needs the delta RPS of the current picture and the index of thereference RPS in order to obtain the RPS to be used in predictivedecoding of the current picture by an inter-RPS method, and thus, thedelta RPS of the current picture that is encoded and the index of thereference RPS need to be added to the bit stream.

The picture decoding apparatus 100 may determine the index of thereference RPS to be referred to in obtaining the RPS to be used inpredictive decoding of the current picture in operation S611. Here, thepicture decoding apparatus 100 may determine the index of the referenceRPS based on encoding efficiency. The reference RPS is pre-defined inthe SPS and may be identified as an index of each RPS.

The picture encoding apparatus 100 may obtain the delta RPS by using theindex of the reference RPS determined in operation S611, in operationS613. The picture encoding apparatus 100 may obtain the reference RPSdefined in the SPS by using the index of the reference RPS and mayobtain the delta RPS by obtaining a difference between the obtainedreference RPS and the RPS to be used in predictive decoding of thecurrent picture.

In addition, a value indicating a reference picture of the reference RPSto which the delta RPS is applied may be defined in operation S613. Forexample, when the reference RPS is {−1, 1, 3, 5}, the RPS to be used inpredictive decoding of the current picture and to be signaled is {−2, 0,2}, and a value of the delta RPS is −1, the determined RPS may have thesame value as the RPS of {−2, 0, 2} only when the delta RPS is notapplied to a POC value of a fourth reference picture when applying thedelta RPS to the reference RPS. Thus, {1, 1, 1, 0} in which a fourthvalue for the fourth reference picture is 0 may be defined as a valueindicating the reference picture to which the delta RPS is applied. Thevalue indicating the reference picture to which the delta RPS is appliedmay be defined and signaled by the first signaling method as well as thesecond signaling method.

The picture encoding apparatus 100 may signal the RPS to be used inprediction decoding of the current picture by encoding the index of thereference RPS and the delta RPS to add to the predetermined domain ofthe bit stream in operation S615.

FIG. 7 is a flowchart illustrating a method of determining an RPSaccording to an exemplary embodiment.

Referring to FIG. 7, the picture decoding apparatus 200 may determinewhether to determine the RPS based on a delta RPS, in order to determinean RPS to be used in predictive decoding of a current picture, inoperation S701.

In operation S703, the picture decoding apparatus 200 may determine theRPS based on a result of the determination of operation S701.

FIG. 8 is a flowchart illustrating a method of determining an RPSaccording to an exemplary embodiment.

Referring to FIG. 8, when the picture decoding apparatus 200 determinesthe RPS based on the delta RPS, the picture decoding apparatus 200 mayobtain a flag indicating whether a first signaling method or a secondsignaling method is used to determine the RPS to be used in predictivedecoding of the current picture, in operation S801.

When the flag is 1 in operation S803, the picture decoding apparatus 200may determine the RPS to be used in predictive decoding of the currentpicture by using the first signaling method.

The picture decoding apparatus 200 may obtain POC values of the currentpicture and a previous picture according to the first signaling method,in operation S805.

The picture decoding apparatus 200 may obtain the delta RPS of thecurrent picture by using the obtained POC value in operation S807. Thatis, the picture decoding apparatus 200 may determine a difference valuebetween the POC value of the current picture and the POC value of theprevious picture as the delta RPS of the RPS to be used in predictivedecoding of the current picture.

The picture decoding apparatus 200 may obtain an RPS used in predictivedecoding of the previous picture, where the RPS is capable of being usedas a reference RPS to obtain the RPS, in operation S809.

The picture decoding apparatus 200 may obtain the RPS by using the deltaRPS and the RPS used in predictive decoding of the previous picture, inoperation S811. That is, the picture decoding apparatus 200 may obtainthe RPS by adding the delta RPS to POC values of reference picturesincluded in the RPS used in predictive decoding of the previous picture.Here, the RPS may be obtained by further using a value indicating thereference picture to which the delta RPS is applied.

Meanwhile, when the flag is 0 in operation S803, the picture decodingapparatus 200 may determine the RPS to be used in predictive decoding ofthe current picture by using the second signaling method.

The picture decoding apparatus 200 may obtain an index of the referenceRPS and the delta RPS from a predetermined domain of a bit stream, inoperation S813.

The picture decoding apparatus 200 may obtain the reference RPS by usingthe index of the reference RPS obtained in operation S813, in operationS815. The reference RPS may be a value pre-defined in an SPS, which maybe identified as an index.

The picture decoding apparatus 200 may determine the RPS to be used inpredictive decoding of the current picture based on the reference RPSand the delta RPS in operation S817. That is, the picture decodingapparatus 200 may obtain the RPS to be used in predictive decoding ofthe current picture by adding the delta RPS to POC values of referencepictures of the reference RPS. Here, the RPS to be used in predictivedecoding of the current picture may be determined based on a valueindicating the reference picture of the reference RPS to which the deltaRPS may be applied.

FIG. 9 is a view of an example of an SPS according to an exemplaryembodiment.

Referring to FIG. 9, num_short_term_ref_pic_sets (1) may be defined inthe SPS as the number of a short term RPS, and short_term_ref_pic_set(i) (3) may be defined in the SPS as much as a value ofnum_short_term_ref_pic_sets (1). As described earlier, an RPS which is aset of reference pictures that are used in predictive decoding of apicture may be defined in the SPS, and each RPS may be identified as anindex.

FIG. 10 is a view of an example of a slice header according to anexemplary embodiment.

Referring to FIG. 10, when the short term RPS is defined in the sliceheader, 0 may be added to a value of short_term_ref_pic_set_flag (5).When the value of short_term_ref_pic_set_sps_flag (5) is 0, the shortterm RPS may be defined in short_term_ref_pic_set(num_short_term_ref_pic_sets) (7) of the slice header. The RPS definedin the slice header may be a value other than the RPS defined in theSPS.

FIG. 11 is a view of an example of a short term RPS according to anexemplary embodiment.

Referring to FIG. 11, the short term RPS that may be defined in theslice header illustrated in FIG. 10 may be defined inshort_term_ref_pic_set (idx).

A value of inter_ref_pic_set_prediction_flag (9) may be determined basedon whether or not the RPS is defined by an inter RPS method.

In the case where, if the value of inter_ref_pic_set_prediction_flag is1 in if(inter_ref_pic_set_prediction_flag) (11), idx isnum_short_term_ref_pic_sets (13), that is, in the case where an index ofthe RPS is the same as the number of the short RPSs defined in the SPS,a value of derived_delta_rps_flag (15) may be determined.

The index of the short term RPS defined in the SPS may have a value in arange of 0 to num_short_term_ref_pic_sets-1. Thus, the case where theindex of the RPS is the same as the number of the short term RPSsdefined in the SPS is the case where an RPS which is not defined in theSPS is defined in the slice header. That is, the value ofderived_delta_rps_flag (15) may be determined in the case where the RPSwhich is not defined in the SPS is defined in the slice header.

The value of derived_delta_rps_flag (15) may correspond to the flag thatmay be obtained by being added to the bit stream according to anexemplary embodiment. Also, the RPS may be signaled based on the valueof derived_delta_rps_flag (15).

In the case where derived_delta_rps_flag (15) is 0 (17), the videodecoding apparatus 200 may obtain the RPS to be used in predictivedecoding of the current picture by using the delta RPS and the index ofthe reference RPS.

In the case where derived_delta_rps_flag (15) is 1, the delta RPS andthe index of the reference RPS may be obtained from delta_idx_minus1(19), delta_rps_sign (21), and abs_delta_rps_minus1 (23) by Equations 1and 2 below.

DeltaRPS=(1−2*delta_rps_sign)*(abs_delta_rps_minus1+1)  [Equation 1]

RIdx=idx−(delta_idx_minus1+1)  [Equation 2]

In Equations 1 and 2, DeltaRPS denotes the delta RPS and RIdx denotesthe index of the reference RPS.

delta_rps_sign (21) may have a value of 0 or 1, and each value maydenote a negative number or a positive number. abs_delta_rps_minus1 (23)is a value in which 1 is subtracted from the delta RPS.

idx denotes an index of the short term RPS defined in the slice header,and delta_idx_minus1 (19) is a delta index value, which is a valueobtained by subtracting 1 from a difference value between the RPS andthe index of the reference RPS.

FIGS. 12A and 12B are views of an example of an RPS of picturesaccording to an exemplary embodiment. FIG. 12A illustrates a framedecoded by a random access in which a decoding order and a POC are notthe same, and FIG. 12B illustrates a frame decoded by a low delay inwhich the decoding order and the POC are the same.

Referring to FIGS. 12A and 12B, the POC 25 and 31, reference pictures 27and 33, and delta RPSs 29 and 35 are indicated for each frame. Framenumbers are in accordance with the decoding order.

The delta RPSs 29 and 35 are each a difference value between POC valuesof reference pictures included in a reference RPS and reference picturesincluded in an RPS to be used in predictive decoding of a currentpicture. Here, the POC values of the reference pictures are on the basisof the current picture of 0. The reference RPS for each frameillustrated in FIG. 12A is an RPS used in predictive decoding of a framepreviously decoded. Thus, referring to the reference pictures 27 and 33,the RPS used in predictive decoding of a previous picture and the RPSused in predictive decoding of the current picture has a difference thatis the same as the delta RPS 29.

For example, the RPS of frame 4 is {−1, 1, 3, 7} and the RPS of frame 5is {−1, −3, 1, 5} in FIG. 12A. Also, the delta RPS of frame 5 is −2.Thus, the RPS of frame 5 may be obtained by adding the delta RPS to RPSof FIG. 4. That is, the RPS of frame 5 may be {−1−2=−3, 1−2=−1, 3−2=1,7−2=5}. However, the case where the delta RPS is added to the POC valueof the RPS may be restricted by a value of reference idcs 30. That is,the RPS to be used in predictive decoding of the current picture may beobtained by adding the delta RPS only to the POC value in which thevalue of the reference idcs 30 is 1. The value of the reference idcs 30and 36 may correspond to a value indicating a reference picture of theRPS to which the delta RPS may be applied.

Meanwhile, when comparing the delta RPSs 29 and 35 and the POC 25 and31, a difference value between the current picture and the previouspicture is the same as the delta RPSs 29 and 35 for each frame. This isbecause a reference picture of the current picture should be a referencepicture of a picture previously output or a reference picture of apicture previously decoded. Thus, according to the one or more of theabove exemplary embodiments, the video decoding apparatus 200 may obtainthe delta RPS of the RPS to be used in predictive decoding of thecurrent picture by using a POC difference value between the picturepreviously decoded and the current picture, without the need of thedelta RPS being explicitly encoded and transferred.

As described above, according to the one or more of the above exemplaryembodiments, the video decoding apparatus 200 may obtain the delta RPSby using the POC difference value between the current picture and theprevious picture, without the need of the delta RPS being explicitlyencoded and transferred via the video encoding apparatus 100, in orderto signal the delta RPS to obtain the RPS to be used in predictivedecoding of the current picture. Therefore, the number of bits encodedin the video encoding apparatus 100 may be reduced.

Exemplary embodiments may also be embodied as computer readable code ona computer readable recording medium. The computer readable recordingmedium is any data storage device that can store data which can bethereafter read by a computer system. Examples of the computer readablerecording medium include read-only memory (ROM), random-access memory(RAM), CD-ROMs, magnetic tapes, floppy disks, optical data storagedevices, etc.

It should be understood that the exemplary embodiments described hereinshould be considered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each exemplaryembodiment should typically be considered as available for other similarfeatures or aspects in other embodiments.

While one or more exemplary embodiments have been described withreference to the figures, it will be understood by those of ordinaryskill in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the inventiveconcept as defined by the following claims.

1. An apparatus of decoding a video, the apparatus comprising: at leastone processor configured to obtain information of the number ofreference picture sets from a bitstream, wherein the reference picturesets are included in a sequence parameter set and a reference pictureset includes a plurality of reference pictures, to determine whether anindex of a current reference picture set of a current picture is equalto the number of reference picture sets, wherein the number of referencepicture sets is based on the information of the number of the referencepicture sets and the index of the current reference picture setindicates the current reference picture set among reference picturesets, when the index of the current reference picture set of the currentpicture is equal to the number of reference picture sets, to obtaindelta index information about a difference between the index of thecurrent reference picture set of the current picture and an index of areference reference picture set (reference RPS) of the current picturefrom the bitstream, to determine the index of the reference RPS based onthe delta index information, to determine the current reference pictureset of the current picture based on the index of the reference RPS ofthe current picture and a delta RPS which is a difference value betweena picture order count (POC) value of a reference picture in the currentreference picture set of the current picture and a picture order count(POC) value of a reference picture in the reference RPS of the currentpicture, to predictive decode the current picture by using a referencepicture included in one of reference picture sets including the currentreference picture set of the current picture, and wherein theinformation of the number of reference picture sets which is obtainedfrom a bitstream is in a sequence parameter set included in thebitstream.
 2. The apparatus of claim 1, wherein a reference picture setis obtained from at least one of a first part of the bitstream and asecond part of the bitstream, wherein the first part is about thesequence parameter set and the second part is about slice header.
 3. Theapparatus of claim 2, wherein an index of a reference picture set, whichis determined based on the first part of the bitstream, is less than thenumber of reference picture sets, and an index of a reference pictureset, which is determined based on the second part of the bitstream, isequal to the number of reference picture sets.
 4. The apparatus of claim2, wherein the delta index information indicates a value obtained bysubtracting 1 from the difference between the index of the currentreference picture set of the current picture and the index of thereference RPS.
 5. The apparatus of claim 2, the reference RPS is areference picture set obtained from the second part of the bitstream. 6.An apparatus of encoding a video, the apparatus comprising: at least oneprocessor configured to determine reference picture sets available topredict a current image, to generate information of the number ofreference picture sets, wherein the reference picture sets are includedin a sequence parameter set, to generate delta index information about adifference between an index of a current reference picture set of thecurrent picture and an index of a reference reference pictureset(reference RPS) and a delta RPS which is a difference value between apicture order count (POC) value of a reference picture in the currentreference picture set of the current picture and a picture order count(POC) value of a reference picture in the reference reference pictureset, wherein the index of the current reference picture set of thecurrent picture indicates the current reference picture set of thecurrent picture among reference picture sets, wherein the delta indexinformation and the delta RPS are generated to be used to determine thecurrent reference picture set of the current picture set when the indexof the current reference picture set of the current picture is equal tothe number of the reference picture sets included in a sequenceparameter set, and to generate a bitstream including the information ofthe number of reference picture sets included in the sequence parameterset, the delta index information and the delta RPS, wherein theinformation of the number of reference picture sets which is obtainedfrom a bitstream is in a sequence parameter set included in thebitstream.
 7. A non-transitory computer-readable storage medium storinga bitstream comprising: information of the number of reference picturesets, wherein the reference picture sets are included in a sequenceparameter set and available to predict a current image; and delta indexinformation about a difference between an index of a current referencepicture set of the current picture and an index of a reference referencepicture set (reference RPS), wherein the index of the current referencepicture set of the current picture indicates the current referencepicture set of the current picture among reference picture sets; and adelta RPS which is a difference value between a picture order count(POC) value of a reference picture in the current reference picture setof the current picture and a picture order count (POC) value of areference picture in the reference RPS of the current picture, whereinthe delta index information and the delta RPS are generated to be usedto determine the current reference picture set of the current picturewhen the index of the current reference picture set of the currentpicture is equal to the number of reference picture sets included in thesequence parameter set, wherein the information of the number ofreference picture sets which is obtained from a bitstream is in asequence parameter set included in the bitstream, and wherein a valueabout the index of the reference reference picture set is smaller than avalue about the index of the current reference picture set.